Human-rights organizations may soon be able to use free satellite technology to spot evidence of abuses in Darfur and elsewhere.

Villages that have been destroyed during conflicts or ethnic cleansing can be spotted from space by satellites, says Erik Prins, a Danish remote-sensing consultant. The low-resolution images, from the Landsat satellite, reveal subtle changes in the albedo, or reflectivity, of towns and villages that have been burned to the ground.

Prins first began studying satellite data of Darfur at the request of the human-rights advocacy group Amnesty International in 2004 — a year after the start of the conflict, which has killed more than 300,000 people and displaced 2.3 million refugees.

His latest research, published in the International Journal of Remote Sensing1, validates the results of his preliminary study for Amnesty2, and shows that the albedo method seems to be highly reliable.

With a resolution of 30 metres, Landsat does not offer high-definition images, but even at this resolution the characteristic structure of villages in Darfur can be identified easily by a trained eye. Burnt villages reflect less light, and this reduced albedo is reliable enough to be detected by software analysis of Landsat data.

Concealed attacks

Satellite images capture the location of a burned village.Eric Prins

Amnesty commissioned the initial study to use satellite imagery - taken in March 2003 and May 2004 for a 32,000-square-kilometre zone of West Darfur — to try to verify eye-witness accounts, from refugees fleeing the region, of concealed mass attacks on civilians.

Independent verification on the ground was impossible, as Darfur was out-of-bounds to the media and to humanitarian groups. It was estimated that 44% of villages in the region had been destroyed over the course of the previous year.

Prins set out to validate the albedo method by comparing a sample of his initial results — covering 352 villages — with high-resolution satellite images published since by the United States Agency for International Development's Humanitarian Information Unit, Google Earth, and Amnesty International.

Around half of the 352 villages showed detectably reduced albedo in 2004 compared with 2003, and the comparison with Google Earth images showed that this finding was 90% accurate. Prins suggests that the Landsat method could be a quick and cheap way to monitor large areas.

Given that Landsat images are freely available, the historical archive could "reveal a lot", says Prins. It could also be used to put together a full picture of the destruction that has taken place in Darfur, he suggests — no comprehensive map of burnt villages in Darfur is yet available.

Huge step

Prins' study has been welcomed by remote-sensing and humanitarian experts. "Such a method could be a huge step in more comprehensive and timely village monitoring," says Michael Graham, head of the Crisis in Darfur project at the United States Holocaust Memorial Museum in Washington DC, which is a joint venture with Google.

"Overall, I think this is great work," agrees Lars Bromley, director of the American Association for the Advancement of Science's Geospatial Technologies and Human Rights project, who has used mostly high-resolution satellite imagery to document human-rights violations in Burma, Zimbabwe and elsewhere. "This sort of analysis may help to verify larger events within a few days or a few weeks after their occurrence," he says.

But the low resolution of Landsat imagery means that whereas most villages can be identified, it misses smaller, more dispersed villages. Bush fires and agricultural burning also generate decreases in albedo. Such fires "often occur right up to the doorstep of villages, making a burned area a difficult thing to assess when conflict is afoot", says Bromley. Prins argues that in his experience it is relatively easy to distinguish such fires from burnt villages.

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"During the wet season the method might have some limitations," says Prins. But "most attacks take place during the dry season when you have more mobility, and cases from the wet period will then be found in the following dry period."

Humanitarian groups are increasingly aware of the potential of remote sensing for monitoring conflicts, but the major obstacles are less technical and more political, says Paul Currion, a UK-based consultant in humanitarian crises. To operate effectively on the ground, humanitarian agencies need to remain apolitical. If they started publishing maps and pointing fingers, they would quickly find themselves "persona non grata" on the ground, he says. "It's unlikely that any of the United Nations agencies or the Red Cross would be able to undertake or associate with something like this unless the results in no way implicated the Sudanese government — which is unlikely."

Disclosure: Declan Butler was a volunteer mapper in the 'Crisis in Darfur' project http://earth.google.com/outreach/cs_darfur.html

References

Prins, E.Int. J. Rem. Sens.29, 1207-1214 (2008).

Amnesty International.Sudan: At the mercy of killers – destruction of villages in Darfur http://www.amnesty.org/en/library/info/AFR54/072/2004 (2004).